Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$115.58	6.513%	$123.1077	$123.11	$123.10	$123.10
Purchase #2	$26.51	12.208%	$29.7463	$29.75	$29.75	$29.70
Purchase #3	$250.82	13.799%	$285.4307	$285.43	$285.45	$285.40
Purchase #4	$56.33	6.327%	$59.894	$59.89	$59.90	$59.90
Purchase #5	$246.27	7.615%	$265.0235	$265.02	$265.00	$265.00
Purchase #6	$169.79	11.682%	$189.6249	$189.62	$189.60	$189.60
Purchase #7	$112.69	4.523%	$117.787	$117.79	$117.80	$117.80
7 purchase totals =	$977.99		$1,070.6141	$1,070.61	$1,070.60	$1,070.50